Optical assembly with evanescent activation light leakage for dimming

ABSTRACT

An optical assembly is configured to receive visible scene light at the backside of the optical assembly and to direct the visible scene light on an optical path toward the eyeward side. The optical assembly includes a dimming layer disposed on the optical path and includes a photochromic material that is configured to darken in response to exposure to a range of light wavelengths. An illumination layer is also disposed on the optical path and is configured to propagate an evanescent activation light within the illumination layer. The illumination layer is also configured to leak the evanescent activation light towards the dimming layer to activate a darkening of the photochromic material of the dimming layer to dim the visible scene light.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. provisional Application No. 63/284,410 filed Nov. 30, 2021, which is hereby incorporated by reference.

TECHNICAL FIELD

Aspects of the present disclosure relate generally to head mounted devices, and in particular but not exclusively, relate to the dimming of a photochromic material included in an optical assembly of the head mounted device.

BACKGROUND INFORMATION

A smart device is an electronic device that typically communicates with other devices or networks. In some situations the smart device may be configured to operate interactively with a user. A smart device may be designed to support a variety of form factors, such as a head mounted device, a head mounted display (HMD), or a smart display, just to name a few.

Smart devices may include one or more electronic components for use in a variety of applications, such as gaming, aviation, engineering, medicine, entertainment, video/audio chat, activity tracking, and so on. In some examples, a smart device, such as a head-mounted device or HMD, may include a display that can present data, information, images, or other virtual graphics while simultaneously allowing the user to view the real world.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.

FIGS. 1A, 1B, and 1C illustrate a user's view through a near-eye optical assembly of a head-mounted device, in accordance with aspects of the disclosure.

FIG. 2 illustrates a head-mounted device, in accordance with aspects of the disclosure.

FIG. 3A illustrates an example portion of an optical assembly, in accordance with aspects of the disclosure.

FIG. 3B illustrates another example portion of an optical assembly, in accordance with aspects of the disclosure.

FIG. 3C illustrates yet another example portion of an optical assembly, in accordance with aspects of the disclosure.

FIG. 4 illustrates an example portion of an optical assembly including one or more optional additional layers, in accordance with aspects of the disclosure.

FIG. 5A illustrates an optical assembly having an illumination layer with multiple edge-mounted illuminators arranged for global dimming, in accordance with aspects of the disclosure.

FIG. 5B illustrates the optical assembly of FIG. 5A with the dimming layer in a dimmed state, in accordance with aspects of the disclosure.

FIG. 6 illustrates an optical assembly with an illumination layer having a reflective coating for containing activation light, in accordance with aspects of the disclosure

FIG. 7 illustrates a portion of a head-mounted device that includes a frame and an optical assembly, in accordance with aspects of the disclosure.

FIG. 8 illustrates an optical assembly having an illumination layer with multiple edge-mounted illuminators arranged for regional dimming of a dimming layer, in accordance with aspects of the disclosure.

FIG. 9 illustrates an example computing device for the dynamic control of edge-mounted illuminators, in accordance with aspects of the present disclosure.

DETAILED DESCRIPTION

Embodiments of an apparatus and method for controlling transmission attenuation in augmented reality are described herein. In the following description, numerous specific details are set forth to provide a thorough understanding of the embodiments. One skilled in the relevant art will recognize, however, that the techniques described herein can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring certain aspects.

Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

In some implementations of the disclosure, the term “near-eye” may be defined as including an element that is configured to be placed within 50 mm of an eye of a user while a near-eye device is being utilized. Therefore, a “near-eye optical element” or a “near-eye system” would include one or more elements configured to be placed within 50 mm of the eye of the user.

In aspects of this disclosure, visible light may be defined as having a wavelength range of approximately 380 nm-700 nm. Non-visible light may be defined as light having wavelengths that are outside the visible light range, such as ultraviolet light and infrared light. Infrared light having a wavelength range of approximately 700 nm-1 mm includes near-infrared light. In aspects of this disclosure, near-infrared light may be defined as having a wavelength range of approximately 700 nm-1.4 μm. Violet light may include light having a wavelength in the range of approximately 380-450 nm.

As mentioned above, a head-mounted device may include a display that is configured to present data, information, images, or other virtual graphics while simultaneously allowing the user to view the real world. However, the virtual graphics may be difficult for the user to view if the environment is too bright, if there is insufficient contrast between the virtual graphics and the user's current view of the real world, if a color of the virtual graphic matches the color of the real world behind the virtual graphic, or some combination thereof. By way of example, FIG. 1A illustrates a user's view of a real-world scene 100 through an optical assembly 102 of a head-mounted device. As shown in FIG. 1A, the optical assembly 102 allows the user to view the real-world scene 100 while simultaneously presenting a virtual graphic 104 to the user. In the illustrated example, virtual graphic 104 is an icon, but in other examples, the virtual graphic 104 may include text, a picture, video, or other visual information that is generated by the optical assembly 102 for presentation to the user. However, as shown in FIG. 1A the virtual graphic 104 is positioned on the optical assembly 102 at the same location as the user's view of a real-world object 106 (e.g., illustrated as a shrub/bush in FIG. 1A). In some examples, the real-world object 106 may interfere with the user's visibility of the virtual graphic 104. That is, the real-world object 106 may be the same or similar color as the virtual graphic 104, and/or the contrast between the real-world object 106 and the virtual graphic 104 may be too low. Thus, in some conditions, the virtual graphic 104 may be difficult for the user to discern when it is co-located with the user's view of the real-world object 106.

Accordingly, aspects of the present disclosure provide for the dimming of light received from the real-world scene 100 to increase the visibility of the virtual graphic 104. For example, FIG. 1B illustrates the darkening of an entire field of view that is provided by the optical assembly 102. In some examples, dimming the entire field of view may be referred to as global dimming. As shown, the dimming provided by the optical assembly 102 reduces or occludes light received from the real-world scene 100 but does not occlude or dim the display light used to generate the virtual graphic 104. Thus, while FIG. 1B illustrates the virtual graphic 104 as being unchanged with respect to the view shown in FIG. 1A, the virtual graphic 104 may have increased visibility due to the darkening of the real-world object 106 provided by the global dimming of the optical assembly 102.

FIG. 1C illustrates an example of optical assembly 102 darkening a region 108, where region 108 is less than the entire field of view provided by the optical assembly 102. In some examples, dimming only a portion of the field-of-view provided by the optical assembly 102 (e.g., less than the entire field-of-view) is referred to as local dimming.

The dimming provided by the optical assembly 102, as shown in FIGS. 1B and 1C, may be provided by a dimming layer included in the optical assembly 102. The dimming layer may include a photochromic material that darkens in response to exposure to a range of light wavelengths. In some aspects, when activated, the photochromic material may undergo a reversible photochemical reaction that results in a change in its visible light absorption, in strength and/or wavelength.

In some embodiments, the darkening of the dimming layer is activated by way of one or more illumination layers that are included in the optical assembly 102. The illumination layers may be disposed adjacent to the dimming layer and are configured to propagate evanescent activation light within the illumination layer received from one or more illuminators (e.g., diodes) mounted on the edge of the illumination layer. The illumination layer is also configured to leak a portion of the evanescent activation light towards the dimming layer to activate the darkening and thus dim the visible scene light. These and other aspects will be discussed in more detail below.

FIG. 2 illustrates an example head-mounted device 200, in accordance with aspects of the present disclosure. A head-mounted device, such as head-mounted device 200, is one type of smart device, typically worn on the head of a user to provide artificial reality content to a user. Artificial reality is a form of reality that has been adjusted in some manner before presentation to the user, which may include, e.g., virtual reality (VR), augmented reality (AR), mixed reality (MR), hybrid reality, or some combination and/or derivative thereof.

The illustrated example of head-mounted device 200 is shown as including a frame 202, temple arms 204A and 204B, and a near-eye optical assembly 206A and a near-eye optical assembly 206B. FIG. 2 also illustrates an exploded view of an example of near-eye optical assembly 206A. Near-eye optical assembly 206A is shown as including a display layer 210, an illumination layer 212, and a dimming layer 218.

As shown in FIG. 2 , frame 202 is coupled to temple arms 204A and 204B for securing the head-mounted device 200 to the head of a user. Example head-mounted device 200 may also include supporting hardware incorporated into the frame 202 and/or temple arms 204A and 204B. The hardware of head-mounted device 200 may include any of processing logic, wired and/or wireless data interfaces for sending and receiving data, graphic processors, and one or more memories for storing data and computer-executable instructions. In one example, head-mounted device 200 may be configured to receive wired power and/or may be configured to be powered by one or more batteries. In addition, head-mounted device 200 may be configured to receive wired and/or wireless data including video data.

FIG. 2 illustrates near-eye optical assemblies 206A and 206B that are configured to be mounted to the frame 202. The frame 202 may house the near-eye optical assemblies 206A and 206B by surrounding at least a portion of a periphery of the near-eye optical assemblies 206A and 206B. The near-eye optical assembly 206A is configured to receive visible scene light 222 at a backside 211 of the near-eye optical assembly 206A and to direct the visible scene light 222 on an optical path towards the eyeward side 209. In some examples, near-eye optical assembly 206A may appear transparent to the user to facilitate augmented reality or mixed reality such that the user can view visible scene light 222 from the environment while also receiving display light 224 directed to their eye(s) by way of display layer 210. In further examples, some or all of the near-eye optical assemblies 206A and 206B may be incorporated into a virtual reality headset where the transparent nature of the near-eye optical assemblies 206A and 206B allows the user to view an electronic display (e.g., a liquid crystal display (LCD), an organic light emitting diode (OLED) display, a micro-LED display, etc.) incorporated in the virtual reality headset.

As shown in FIG. 2 , the display layer 210 is disposed on the optical path of the near-eye optical assembly 206A, between the eyeward side 209 and the backside 211 of the near-eye optical assembly 206A. In particular, the display layer 210 is disposed between the eyeward side 209 and the illumination layer 212. In some examples, display layer 210 may include a waveguide 216 that is configured to direct display light 224 to present one or more virtual graphics to an eye of a user of head-mounted device 200. In some aspects, waveguide 216 is configured to direct display light 224 that is generated by an electronic display to the eye of the user. In some implementations, at least a portion of the electronic display is included in the frame 202 of the head-mounted device 200. The electronic display may include an LCD, an organic light emitting diode (OLED) display, micro-LED display, pico-projector, or liquid crystal on silicon (LCOS) display for generating the display light 224.

As shown in FIG. 2 , illumination layer 212 is on the optical path of the near-eye optical assembly 206 between the eyeward side 209 and the dimming layer 218. FIG. 2 also shows the illumination layer 212 as including one or more illuminators 214 that are coupled to an edge 213 (i.e., periphery) of the illumination layer 212. The illuminator 214 is configured to selectively emit an evanescent activation light 226 a that propagates within the illumination layer 212. In some aspects, the illumination layer 212 is configured to leak at least a portion of the evanescent activation light 226 b towards the dimming layer 218 to activate a darkening of the photochromic material. In some examples, the evanescent activation light 226 a is within the range of light wavelengths that activate the photochromic material of the dimming layer 218 (e.g., IR light, UV light, violet light, etc.).

In some aspects the illuminator 214 may be a light source that generates the evanescent activation light 226 a, such as a light emitting diode, a micro light emitting diode (micro-LED), an edge emitting LED, a vertical cavity surface emitting laser (VCSEL) diode, or a Superluminescent diode (SLED).

FIG. 2 also illustrates the dimming layer 218 as being disposed on the optical path of the near-eye optical assembly 206A, between the eyeward side 209 and the backside 211. In particular, the dimming layer 218 is shown as being disposed between the display layer 210 and the backside 211. In some examples, the dimming layer 218 includes a photochromic material that is configured to darken in response to exposure to a range of light wavelengths. For example, the photochromic material may be configured to undergo a reversible photochemical reaction in response to exposure to non-visible light, such as infrared (IR) and/or ultraviolet (UV) light. In other examples, the photochromic material may be activated to darken in response to exposure to violet light having wavelengths in the range of 400 to 440 nm. In some aspects, the photochromic material is a film or dye that is applied to a transparent material, such as a plastic or glass lens. In other aspects, the photochromic material is provided by a photochromic compound that is suspended within a transparent substrate, such as a plastic or glass lens.

In some aspects, the photochromic material of the dimming layer 218 is distributed across the entire field-of-view provided by the near-eye optical assembly 206A (e.g., across the entire dimming layer 218). In other aspects, the photochromic material may be provided in only certain portions of the field-of-view (e.g., upper half of the dimming layer 218).

In some examples, the dimming layer 218 and/or the illumination layer 212 may have a curvature for focusing light (e.g., scene light 222) to the eye of the user. Thus, the dimming layer 218 and illumination layer 212 may, in some examples, may be referred to as a lens. In some aspects, the dimming layer 218 and the illumination layer 212 may have a thickness and/or curvature that corresponds to the specifications of a user. In other words, the dimming layer 218 and/or illumination layer 212 may be a prescription lens.

As mentioned above, the illuminator 214 of the illumination layer 212 is configured to emit the evanescent activation light 226 a to propagate within the illumination layer 212, which leaks out towards the dimming layer 218 to activate a darkening of the photochromic material of the dimming layer 218. In some examples, enabling of the illuminator 214 is dynamically determined by a computing device of the head-mounted device 200. For instance, the head-mounted device 200 may include a computing device that determines whether the visible scene light 222 will interfere with the visibility of a virtual graphic generated by the visible display light 224. The computing device may make such a determination based on a comparison of a color of the visible scene light 222 and/or by determining a contrast between the visible scene light 222 and the visible display light 224. If the color of the visible scene light 222 is the same or similar to the color of the visible display light 224, and/or if the contrast between the visible scene light 222 and the visible display light 224 is lower than a low-contrast threshold, then the computing device may enable the illuminator 214 to emit the activation light 226 a to darken the photochromic material of dimming layer 218.

In some aspects, the photochemical reaction of the dimming layer 218 that is induced by the activation light 226 b may be reversible. In one embodiment, disabling the illuminator 214, such that it no longer emits the activation light 226 b, allows the photochromic material of the dimming layer 218 to naturally revert to its previous non-darkened state. In other embodiments, the head-mounted device 200 may be configured to actively restore the dimming layer 218 to its non-darkened state (un-dimmed) by directing a bleaching light to the dimming layer 218. In some examples, the bleaching light may be emitted by the illuminator 214 or by other light sources (not explicitly shown) that are included in the head-mounted device 200. The bleaching light may be light having a wavelength that increases the rate at which the photochromic material is restored to its non-darkened state, such as visible light, UV light, and/or IR light.

FIG. 3A illustrates an example portion 300A of an optical assembly, in accordance with aspects of the disclosure. The portion 300A of the optical assembly is shown in FIG. 3A as including a dimming layer 302, an illumination layer 304 a, and an illuminator 306. The dimming layer 302, illumination layer 304 a, and illuminator 306, as shown in FIG. 3A, are possible implementations of the dimming layer 218, illumination layer 212, and illuminator 214, respectively, of FIG. 2 . Illumination layer 304 a is shown as including a core layer 308 and an eyeward side cladding layer 310. In the illustrated example of FIG. 3A, the dimming layer 302 is disposed on an optical path between the eyeward side 209 and the backside 211 of the optical assembly. Illumination layer 304 a is shown as being disposed on the optical path between the eyeward side 209 and the dimming layer 302.

In some aspects, dimming layer 218 is a coating of photochromic material that is applied to an optical surface, such as surface 313 of the core layer 308. In another example, dimming layer 218 is a coating of photochromic material that is applied to the optical surface of a transparent substrate (e.g., glass, plastic, etc.) that is optically coupled to the surface 313. In yet another example, dimming layer 302 includes a dye embedded within a transparent substrate, where the embedded dye includes photochromic material that is distributed within the transparent substrate, such as during molding or casting.

FIG. 3A further illustrates illuminator 306 coupled to an edge 305 corresponding to a periphery of the core layer 308. As discussed above, the illuminator 306 may be a light source that is configured to generate evanescent activation light 226 a that is guided within the core layer 308, in part, by total internal reflection (TIR). That is, in the illustrated example, eyeward side cladding layer 310 may be disposed on the surface 311 of the core layer 308 to promote TIR of the evanescent activation light 226 a within the core layer 308. In some implementations the evanescent activation light 226 a undergoes multiple rounds of reflection inside the core layer 308. However, as shown in example of FIG. 3A, the core layer 308 is disposed directly on a surface 315 of the dimming layer 302. For example, the optical interface between dimming layer 302 and illumination layer 304 a may be provided by mating surface 313 of the core layer 308 with the surface 315 of the dimming layer 302 (i.e., without an additional cladding layer). In operation, the optical interface between the illumination layer 304 a and the dimming layer 302 allows leakage of at least a portion of evanescent activation light 226 b towards the dimming layer 302. Thus, the multiple bounces of the evanescent activation light 226 a within the core layer 308 and the resultant leakage evanescent activation light 226 b may trigger the photochromic material of the dimming layer 302 to darken. In some examples, the wavelength of the evanescent activation light 226 a and 226 b matches a peak of the photochromic material's absorption spectra.

FIG. 3B illustrates another example portion 300B of an optical assembly, in accordance with aspects of the disclosure. In the illustrated example of FIG. 3B, illumination layer 304 b is shown as including an optional backside cladding layer 314. In particular, FIG. 3B illustrates backside cladding layer 314 as being disposed on the surface 313 of the core layer 308 between the core layer 308 and the dimming layer 302. In some aspects, the backside cladding layer 314 is configured to allow at least some leakage of the evanescent activation light 226 b. Thus, in some implementations, the refractive indices (i.e., n1, n2, and n3) of the core layer 308, the eyeward side cladding layer 310, and the backside cladding layer 314 may be configured to promote reflection of the evanescent activation light 226 a at the interface between the core layer 308 and the eyeward side cladding layer 310, while also allowing at least some leakage of the evanescent activation light 226 b at the interface between the core layer 308 and the backside cladding layer 314. In some aspects, the refractive index n1 of the core layer is greater than the refractive index n3 of the backside cladding layer 314, and the refractive index n3 is greater than the refractive index n2 of the eyeward side cladding layer 310.

FIG. 3C illustrates yet another example portion 300C of an optical assembly, in accordance with aspects of the disclosure. In the illustrated example of FIG. 3C, the eyeward side cladding layer 310 is shown as having a thickness 317, whereas the optional backside cladding layer 314 is shown as having a different thickness 319. In some aspects, the thickness 319 of the backside cladding layer 314 is configured to allow at least some leakage of the evanescent activation light 226 b. In some implementations, thickness 319 of the backside cladding layer 314 is less than the thickness 317 of the eyeward side cladding layer 310. In some aspects, thickness 319 of the backside cladding layer 310 may be in the range of one to ten microns.

FIG. 4 illustrates an example portion 400 of an optical assembly including one or more optional additional layers, in accordance with aspects of the disclosure. In particular, FIG. 4 illustrates the optical assembly as including optional absorption layers 402 a and 402 b, as well as optional encapsulation layers 404A and 404 b. In some, aspects the absorption layers 402 and 402 b are disposed within the optical assembly on the optical path between the eyeward side 209 and the backside 211 to absorb evanescent activation light 226 a and 226 b to prevent or reduce leakage of the activation light out of the optical assembly. In the illustrated example, absorption layer 402 a is disposed between the eyeward side cladding layer 310 and the eyeward side 209 of the optical assembly, whereas absorption layer 402 b is disposed between the dimming layer 302 and the backside 211 of the optical assembly. In some implementations, the encapsulation layers 404 a and 404 b may be disposed on an outermost surface of the illumination and dimming layers to provide scratch resistance and/or to provide structural support.

FIG. 5A illustrates an optical assembly 500 having an illumination layer with edge-mounted illuminators 502, 504, 506, and 508 arranged for global dimming, in accordance with aspects of the disclosure. As shown in FIG. 5A, illuminators 502-508 are mounted on a periphery edge 505 of the illumination layer. Although FIG. 5A illustrates the illumination layer as including four illuminators 502-508, any number of illuminators may be provided by the illumination layer, including one or more. In some instances, the illuminators 502-508 are positioned on the edge 505 to direct evanescent activation light into the illumination layer to achieve global dimming (i.e., across the field of view). By way of example, FIG. 5B illustrates the global dimming of the dimming layer provided by illuminators 502-508 emitting evanescent activation light 226 a. In some implementations, the evanescent activation light 226 a propagates through the dimming element but may eventually leak out through the edge 505. Thus, in some examples, the intensity of the activation light 226 a that is generated by the illuminators 502-508 is set to be greater that an activation threshold needed for the photochromic material to darken. In other examples, a reflective coating may be included on the edges of the dimming element to reduce or prevent leakage of the evanescent activation light 226 a. By of example, FIG. 6 illustrates an illumination layer 600 having a reflective coating 602 for containing activation light 226 a, in accordance with aspects of the disclosure. As shown in FIG. 6 , the reflective coating 602 is disposed on an edge 605 (i.e., periphery) of the illumination layer 600 and may be configured to reflect activation light 226 a within the illumination layer 600. In some examples, the reflective coating 602 is minimally transmissive to the range of wavelengths corresponding to the activation light 226 a.

Although the reflective coating 602 may be minimally transmissive to the evanescent activation light 226 a, in operation, some evanescent activation light 226 a may continue to leak at the edges, primarily at the locations corresponding to the illuminators 502-508, themselves. Accordingly, in some examples, the frame in which the optical assembly is to be placed may be configured to absorb or block evanescent activation light 226 a that continues to escape at the edges of the illumination layer. For example, FIG. 7 illustrates a portion 700 of a head-mounted device that includes a frame 702 and illumination layer 600, in accordance with aspects of the disclosure. As shown, the frame 702 may be configured to completely encompass or cap the illumination layer 600 at its periphery to block or absorb any leaking evanescent activation light 226 a at the edges.

FIG. 8 illustrates an illumination layer 800 with multiple edge-mounted illuminators 802 and 804 arranged for regional dimming, in accordance with aspects of the disclosure. Illumination layer 800 is one possible implementation of illumination layer 212 of FIG. 2 . As shown in FIG. 8 , illuminators 802-804 are mounted on a periphery edge of the illumination layer 800. Although FIG. 800 illustrates illumination layer 800 as including two illuminators 802-804, any number of illuminators may be provided by the illumination layer 800, including one or more. In some instances, the illuminators 802-804 are positioned on the edge of illumination layer 800 to direct evanescent activation light into the illumination layer 800 such that leakage of the evanescent activation light towards the dimming layer causes regional dimming (i.e., less than the entire field of view). By way of example, FIG. 8 illustrates the regional dimming provided by illuminators 802-804 emitting activation light 226 a to darken region 806.

FIG. 9 illustrates an example computing device 902 for the dynamic control of edge-mounted illuminators, in accordance with aspects of the present disclosure. The illustrated example of computing device 902 is shown as including a communication interface 904, one or more processors 906, hardware 908, and a memory 910. In one example, one or more of the components illustrated in FIG. 9 may be incorporated into the frame 202 and/or temple arms 204A/204B of the head-mounted device 200 of FIG. 2 . In other examples, one of more of the components illustrated in FIG. 9 may be incorporated into a remote computing device that is communicatively coupled to the head-mounted device 200 for performing one or more aspects of the dynamic control of the illuminators.

The communication interface 904 may include wireless and/or wired communication components that enable the computing device 902 to transmit data to and receive data from other networked devices. The hardware 908 may include additional hardware interface, data communication, or data storage hardware. For example, the hardware interfaces may include a data output device (e.g., electronic display, audio speakers), and one or more data input devices.

The memory 910 may be implemented using computer-readable media, such as computer storage media. In some aspects, computer-readable media may include volatile and/or non-volatile, removable and/or non-removable media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules, or other data. Computer-readable media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD), high-definition multimedia/data storage disks, or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other non-transmission medium that can be used to store information for access by a computing device.

The processors 906 and the memory 910 of the computing device 902 may implement a display module 912 and a dimming control module 914. The display module 912 and the dimming control module 914 may include routines, program instructions, objects, and/or data structures that perform particular tasks or implement particular abstract data types. The memory 910 may also include a data store (not shown) that is used by the display module 912 and/or dimming control module 914.

The display module 912 may be configured to determine that the visible scene light (e.g., visible scene light 222 of FIG. 2 ) of the near-eye optical assembly will interfere with a visibility of a virtual graphic (e.g., virtual graphic 104 of FIG. 1 ) that is generated by the visible display light 224. In some implementations, the head-mounted device may include one or more light sensors that provide information about the visible scene light (e.g., brightness, contrast, color, etc.). In another implementation, the head-mounted device may include a camera that is positioned (e.g., on the temple arm 204B of FIG. 2 ) to obtain images of the field-of-view provided by the optical assembly. The display module 912 may receive the images and/or data from the light sensor to determine whether the visible scene light is interfering with a visibility of the virtual graphic.

In some aspects, the display module 912 determines the visibility of the virtual graphic based on readings obtained from the light sensors and/or by performing image processing on images of the field-of-view. This may include determining an ambient brightness and/or determining a contrast between the visible scene light and the virtual graphic. In another example, the display module 912 may determine the visibility of the virtual graphic by comparing a color of the visible scene light in a region that corresponds to where the virtual graphic is to be displayed. If the visible scene light is too bright, the contrast between the scene light and the virtual graphic is too low, and/or if a color of the scene light is similar to that of the virtual graphic, then the display module 912 then determines that the visible scene light will indeed interfere with the visibility of the virtual graphic.

In response the determination by the display module 912 that the visible scene light will interfere with the visibility of the virtual graphic, the dimming control module 914 may then activate the darkening of one or more regions of the dimming layer of the near-eye optical assembly to dim and/or occlude the visible scene light. For example, with reference to head-mounted device 200 of FIG. 2 , the dimming control module 914 may enable illuminator 214 to emit the evanescent activation light 226 s to activate the darkening of dimming layer 218. As discussed above, the darkening of the dimming layer 218 may dim the visible scene light 222 to increase the visibility of the virtual graphic generated by display light 224.

Embodiments of the invention may include or be implemented in conjunction with an artificial reality system. Artificial reality is a form of reality that has been adjusted in some manner before presentation to a user, which may include, e.g., a virtual reality (VR), an augmented reality (AR), a mixed reality (MR), a hybrid reality, or some combination and/or derivatives thereof. Artificial reality content may include completely generated content or generated content combined with captured (e.g., real-world) content. The artificial reality content may include video, audio, haptic feedback, or some combination thereof, and any of which may be presented in a single channel or in multiple channels (such as stereo video that produces a three-dimensional effect to the viewer). Additionally, in some embodiments, artificial reality may also be associated with applications, products, accessories, services, or some combination thereof, that are used to, e.g., create content in an artificial reality and/or are otherwise used in (e.g., perform activities in) an artificial reality. The artificial reality system that provides the artificial reality content may be implemented on various platforms, including a head-mounted display (HMD) connected to a host computer system, a standalone HMD, a mobile device or computing system, or any other hardware platform capable of providing artificial reality content to one or more viewers.

The above description of illustrated embodiments of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize.

These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation. 

What is claimed is:
 1. An optical assembly, comprising: an eyeward side and a backside, wherein the optical assembly is configured to receive visible scene light at the backside of the optical assembly and to direct the visible scene light on an optical path toward the eyeward side; a dimming layer disposed on the optical path between the eyeward side and the backside, wherein the dimming layer includes a photochromic material that is configured to darken in response to exposure to a range of light wavelengths; and an illumination layer disposed on the optical path between the eyeward side and the dimming layer, wherein the illumination layer is configured to propagate an evanescent activation light that is within the range of light wavelengths, and wherein the illumination layer is configured to leak the evanescent activation light towards the dimming layer to activate a darkening of the photochromic material to dim the visible scene light.
 2. The optical assembly of claim 1, wherein the illumination layer comprises: a core layer configured to propagate the evanescent activation light, the core layer having a first surface facing the eyeward side and a second surface facing the backside; and an eyeward side cladding layer disposed on the first surface of the core layer to promote total internal reflection of the evanescent activation light within the core layer.
 3. The optical assembly of claim 2, wherein the second surface of the core layer is disposed directly on a surface of the dimming layer.
 4. The optical assembly of claim 2, wherein the illumination layer further comprises: a backside cladding layer disposed on the second surface of the core layer between the core layer and the dimming layer, wherein the backside cladding layer has a thickness that is less than a thickness of the eyeward side cladding layer.
 5. The optical assembly of claim 4, wherein the thickness of the backside cladding layer is in the range of one to ten microns.
 6. The optical assembly of claim 2, wherein the illumination layer further comprises: a backside cladding layer disposed on the second surface of the core layer between the core layer and the dimming layer, wherein the backside cladding layer has a refractive index that is greater than a refractive index of the eyeward side cladding layer.
 7. The optical assembly of claim 1, further comprising at least one absorption layer disposed on the optical path between the eyeward side and the backside to absorb the evanescent activation light.
 8. The optical assembly of claim 1, further comprising: at least one illuminator coupled to an edge of the illumination layer, wherein the at least one illuminator is configured to selectively emit the evanescent activation light.
 9. The optical assembly of claim 8, further comprising a reflective coating disposed on the edge of the illumination layer, wherein the reflective coating is configured to reflect the evanescent activation light within the dimming layer.
 10. The optical assembly of claim 1, wherein the evanescent activation light comprises non-visible light, ultraviolet light, infrared light, or violet light.
 11. The optical assembly of claim 1, further comprising: a display layer disposed on the optical path between the eyeward side of the optical assembly and the dimming layer, wherein the display layer is configured to direct visible display light toward the eyeward side.
 12. A head-mounted device, comprising: a frame; and an optical assembly secured within the frame, wherein the optical assembly is configured to receive visible scene light at a backside of the optical assembly and to direct the visible scene light on an optical path toward an eyeward side of the optical assembly, wherein the optical assembly includes: a dimming layer disposed on the optical path between the eyeward side and the backside, wherein the dimming layer includes a photochromic material that is configured to darken in response to exposure to a range of light wavelengths; and an illumination layer disposed on the optical path between the eyeward side and the dimming layer, wherein the illumination layer is configured to propagate an evanescent activation light that is within the range of light wavelengths, and wherein the illumination layer is configured to leak the evanescent activation light towards the dimming layer to activate a darkening of the photochromic material to dim the visible scene light.
 13. The head-mounted device of claim 12, wherein the illumination layer comprises: a core layer configured to propagate the evanescent activation light, the core layer having a first surface facing the eyeward side and a second surface facing the backside; and an eyeward side cladding layer disposed on the first surface of the core layer to promote total internal reflection of the evanescent activation light within the core layer.
 14. The head-mounted device of claim 13, wherein the second surface of the core layer is disposed directly on a surface of the dimming layer.
 15. The head-mounted device of claim 13, wherein the illumination layer further comprises: a backside cladding layer disposed on the second surface of the core layer between the core layer and the dimming layer, wherein the backside cladding layer has a thickness that is less than a thickness of the eyeward side cladding layer.
 16. The head-mounted device of claim 13, wherein the illumination layer further comprises: a backside cladding layer disposed on the second surface of the core layer between the core layer and the dimming layer, wherein the backside cladding layer has a refractive index that is greater than a refractive index of the eyeward side cladding layer.
 17. The head-mounted device of claim 12, wherein the optical assembly further comprises: a display layer disposed on the optical path between the eyeward side of the optical assembly and the dimming layer, wherein the display layer is configured to direct visible display light toward the eyeward side.
 18. An optical assembly, comprising: a dimming layer that includes a photochromic material configured to darken in response to exposure to a range of light wavelengths; an illumination layer coupled to the dimming layer, wherein the illumination layer includes: a core layer configured to propagate an evanescent activation light that is within the range of light wavelengths; and a first cladding layer disposed on a first surface of the core layer to promote total internal reflection of the evanescent activation light within the core layer; and an illuminator coupled to edge of the illumination layer, wherein the illuminator is configured to selectively emit the evanescent activation light, and wherein the illumination layer is configured to leak the evanescent activation light towards the dimming layer to activate a darkening of the photochromic material.
 19. The optical assembly of claim 18, wherein the illumination layer further comprises: a second cladding layer disposed on a second surface of the core layer, opposite the first surface, between the core layer and the dimming layer, wherein the second cladding layer has a thickness that is less than a thickness of the first cladding layer.
 20. The optical assembly of claim 18, wherein the illumination layer further comprises: a second cladding layer disposed on a second surface of the core layer, opposite the first surface, between the core layer and the dimming layer, wherein the second cladding layer has a refractive index that is greater than a refractive index of the first cladding layer. 